1. Field of the Invention
The invention relates to a method for imaging test objects by means of electromagnetic waves, in particular for inspecting individuals for suspicious items, in which the test object is illuminated with electromagnetic waves, and the scattered waves are received and analyzed using the synthetic aperture principle (SAR) to display an image of the test object.
2. Description of the Background Art
In order to inspect individuals or pieces of luggage (hereinafter referred to as test objects) for hidden dangerous items (weapons, explosives), methods are known in which the test objects (individuals, pieces of luggage) are scanned with millimeter waves in order to detect suspicious items. U.S. Pat. No. 5,859,609 describes such a method in which the individual to be inspected stands on a platform while being successively illuminated along his circumference with millimeter waves from a vertical antenna array. To this end, the antenna array travels in a circle around the individual and scans him circumferentially. Electrical signals are produced at a variety of predetermined positions in space from the waves reflected from the target, and a computer generates a holographic reconstruction of the target from these signals. Similar methods are described in U.S. Pat. No. 5,455,590 and EP-A 0925517.
German patent application 10 2005 016 106 describes a method of the generic type in which a test object is illuminated successively with millimeter waves along its circumference, and the scattered waves are received and analyzed to display an image of the test object, wherein the pulse radar or FMCW radar principle is used to analyze radiation scattered in the direction of the longitudinal axis of the test object and the SAR principle is used for analysis perpendicular to the longitudinal axis.
The prior art systems have a number of disadvantages, however. Devices that accomplish beam deflection by phase-shifted driving of an antenna array are very complex and expensive. Moreover, these systems are limited to certain frequency ranges by the geometry of the antenna array. In addition, the resolution and achievable depth information are not satisfactory for inspecting individuals for suspicious items.